BAD as a prototype for a novel therapeutic agent for the treatment of acute leukemia

Inhibitors of Bcl-2 may be useful therapeutic agents for the treatment of a wide variety of malignancies including leukemia. A potential prototype of such a compound is the endogenous Bcl-2 and Bcl-xL binding protein BAD. Previous reports indicate that BAD can overcome the anti-apoptotic effect of Bcl-xL but not Bcl-2. If BAD cannot induce apoptosis in cells over-expressing Bcl-2, it would limit the application of molecules like BAD as novel anti-tumor agents. We reported that transient transfection of BAD induced cell death in cells with and without over-expression of Bcl-2 or Bcl-xL and thereby validated the pursuit of molecules like BAD as novel therapeutic agents.; Small cytotoxic peptides that mimic BAD and overcome Bcl-2 mediated drug resistance may be useful in the treatment of malignant disease. One example is the BH3 domain of BAD that binds and inhibits Bcl-2 and Bcl-xL. A cell permeable version of the peptide was created by fusing it to cpm, a decanoic fatty acid internalization sequence. This fusion peptide induced rapid cell death and apoptosis. However, its cytotoxicity was significantly impaired by the over expression of Bcl-xL, which could limit the usefulness of this compound in treating malignancies with increased levels of Bcl-2 and Bcl-xL. Therefore, enhancing the ability of the BH3 domain of BAD to kill cells over-expressing these survival factors might be therapeutically useful. One strategy to enhance its toxicity is to capitalize on the inherent alpha helical shape of the peptide, since some amphipathic alpha helices are potent naturally occurring antibiotics capable disrupting negatively charged membranes.; We harnessed the alpha helical properties of the BH3 domain of BAD by fusing it to the Antennapedia internalization sequence. We created a 37 amino acid fusion peptide corresponding to the 21 amino acids of the human BH3 domain of BAD fused to the C-terminus of the 16 amino acids of the ANT peptide (ANTBH3BAD). The ANTBH3BAD fusion peptide induced rapid cell death and apoptosis. Its alpha helical secondary structure disrupted mitochondrial function and allowed the peptide to overcome Bcl-2 over-expression and caspase inhibitors.